While I don't think every PM has to be a noteworthy blogger to have a successful career, I do think Jon's principle of conservation of keystrokes is an important one. By far the biggest problem I see on teams of > 1 is communication. Different people know different information, this leads to disconnects and often to product design, quality and schedule issues.

Teams need better communication and PMs are primarily responsible for this. So think about the email you are getting ready to write... Should you add a tester or dev to that email? better yet, should you use a team alias? What info should flow up to your management chain or across to your peers? can you forward that mail? And to Jon's point, can you just blog it and share it with the world?

As Jon mentions, there is a time and a place for private communications, but generally we tend to overuse them.